In an installation having an opening, a screen, which may be a supple screen body or a rigid or semi-rigid panel, is displaced opposite the opening in order to selectively obturate the latter. In order to make the movement of the screen automatic, it has been proposed in the past to equip it with means for automatically detecting a position and/or a displacement of the screen and thus to use pre-defined positions to control electrical power supply to a screen drive motor, particularly the top and bottom ends of stroke and possibly intermediate positions in which the electrical supply to the motor is interrupted or modified in order to stop the screen or vary its speed and/or its drive torque.
An example of such an automatic drive device is given in FR-A-2 654 229.
Although the afore-mentioned device is satisfactory as to its function of automatic control of the drive of the screen, it presents a drawback concerning its tightness or sealing of components, particularly the tightness or sealing of the electronic processing unit that it contains with respect to the ambient environment. In effect, this type of device is likely to be installed outside and thus to be subjected to bad weather. This results in considerable risks of water infiltrating inside the tube and therefore reaching the electronic processing unit and the electric motor, particularly via the opening necessary for the kinematic links between a transmission means and a ring that rotatably supports the tube. It is difficult to seal this opening tight due to the mobility of the ring which, in addition, must present axial and radial clearances sufficient in order, on one hand, to match winding tubes of various origins whose dimensions are imprecise due to their mode of manufacture and, on another hand, to compensate for clearances of expansion associated with the functioning of the motor and climatic conditions.
In order to overcome this problem, one or more O-rings may be interposed between the ring and the fixed head and it may be attempted to adjust the ring around the fixed head as best possible. Furthermore, as described in EP-A-0 965 724, a ring of magnets of alternate polarities may be mounted around a circular support. These solutions are not economical as they require more voluminous parts, particular geometries at the level of the elements in contact and/or a complex process of assembly. In the device known from EP-A-0 965 724, the ring of magnets is expensive and the precision of measurement depends on the angular deviation between the peripheral magnets. This deviation being fixed by the diameter of the support which depends on the type of motor used, it cannot be adjusted easily.
In the domain of automatically controlled electric motors, U.S. Pat. No. 4,952,830 proposes embedding in an appropriate resin electronic sensors for detecting the displacement of the rotor of a motor, these sensors being kinematically linked to the stator. The tightness of the sensors is thus ensured but this solution does not guarantee tightness of the conductors connecting the sensors to an electronic unit for processing the signals furnished by these sensors. In other words, the potential problems of tightness do not affect the sensors as such but concern the more remote electronic components of the processing unit.
It is an object of the present invention to propose a device of the afore-mentioned type, in which the parts of the device sensitive to water are efficiently protected, particularly the electronic components of this device.